1.\" Copyright (c) 1983, 1991, 1993
2.\" The Regents of the University of California. All rights reserved.
3.\"
4.\" Redistribution and use in source and binary forms, with or without
5.\" modification, are permitted provided that the following conditions
6.\" are met:
7.\" 1. Redistributions of source code must retain the above copyright
8.\" notice, this list of conditions and the following disclaimer.
9.\" 2. Redistributions in binary form must reproduce the above copyright
10.\" notice, this list of conditions and the following disclaimer in the
11.\" documentation and/or other materials provided with the distribution.
| 1.\" Copyright (c) 1983, 1991, 1993
2.\" The Regents of the University of California. All rights reserved.
3.\"
4.\" Redistribution and use in source and binary forms, with or without
5.\" modification, are permitted provided that the following conditions
6.\" are met:
7.\" 1. Redistributions of source code must retain the above copyright
8.\" notice, this list of conditions and the following disclaimer.
9.\" 2. Redistributions in binary form must reproduce the above copyright
10.\" notice, this list of conditions and the following disclaimer in the
11.\" documentation and/or other materials provided with the distribution.
|
12.\" 4. Neither the name of the University nor the names of its contributors
| 12.\" 3. Neither the name of the University nor the names of its contributors
|
13.\" may be used to endorse or promote products derived from this software
14.\" without specific prior written permission.
15.\"
16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26.\" SUCH DAMAGE.
27.\"
28.\" @(#)random.3 8.1 (Berkeley) 6/4/93
| 13.\" may be used to endorse or promote products derived from this software
14.\" without specific prior written permission.
15.\"
16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26.\" SUCH DAMAGE.
27.\"
28.\" @(#)random.3 8.1 (Berkeley) 6/4/93
|
29.\" $FreeBSD: head/lib/libc/stdlib/random.3 249035 2013-04-02 23:41:20Z delphij $
| 29.\" $FreeBSD: head/lib/libc/stdlib/random.3 251672 2013-06-13 00:19:30Z emaste $
|
30.\"
31.Dd April 2, 2013
32.Dt RANDOM 3
33.Os
34.Sh NAME
35.Nm random ,
36.Nm srandom ,
37.Nm srandomdev ,
38.Nm initstate ,
39.Nm setstate
40.Nd better random number generator; routines for changing generators
41.Sh LIBRARY
42.Lb libc
43.Sh SYNOPSIS
44.In stdlib.h
45.Ft long
46.Fn random void
47.Ft void
48.Fn srandom "unsigned long seed"
49.Ft void
50.Fn srandomdev void
51.Ft char *
52.Fn initstate "unsigned long seed" "char *state" "long n"
53.Ft char *
54.Fn setstate "char *state"
55.Sh DESCRIPTION
56.Bf -symbolic
57The functions described in this manual page are not cryptographically
58secure.
59Cryptographic applications should use
60.Xr arc4random 3
61instead.
62.Ef
63.Pp
64The
65.Fn random
66function
67uses a non-linear additive feedback random number generator employing a
68default table of size 31 long integers to return successive pseudo-random
69numbers in the range from 0 to
70.if t 2\u\s731\s10\d\(mi1.
71.if n (2**31)\(mi1.
72The period of this random number generator is very large, approximately
73.if t 16\(mu(2\u\s731\s10\d\(mi1).
74.if n 16*((2**31)\(mi1).
75.Pp
76The
77.Fn random
78and
79.Fn srandom
80functions have (almost) the same calling sequence and initialization properties as the
81.Xr rand 3
82and
83.Xr srand 3
84functions.
85The difference is that
86.Xr rand 3
87produces a much less random sequence \(em in fact, the low dozen bits
88generated by rand go through a cyclic pattern.
89All the bits generated by
90.Fn random
91are usable.
92For example,
93.Sq Li random()&01
94will produce a random binary
95value.
96.Pp
97Like
98.Xr rand 3 ,
99.Fn random
100will by default produce a sequence of numbers that can be duplicated
101by calling
102.Fn srandom
103with
104.Ql 1
105as the seed.
106.Pp
107The
108.Fn srandomdev
109routine initializes a state array using
110pseudo-random numbers obtained from the kernel.
111Note that this particular seeding
112procedure can generate states which are impossible to reproduce by
113calling
114.Fn srandom
115with any value, since the succeeding terms in the
116state buffer are no longer derived from the LC algorithm applied to
117a fixed seed.
118.Pp
119The
120.Fn initstate
121routine allows a state array, passed in as an argument, to be initialized
122for future use.
123The size of the state array (in bytes) is used by
124.Fn initstate
125to decide how sophisticated a random number generator it should use \(em the
126more state, the better the random numbers will be.
127(Current "optimal" values for the amount of state information are
1288, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
129the nearest known amount.
130Using less than 8 bytes will cause an error.)
131The seed for the initialization (which specifies a starting point for
132the random number sequence, and provides for restarting at the same
133point) is also an argument.
134The
135.Fn initstate
136function
137returns a pointer to the previous state information array.
138.Pp
139Once a state has been initialized, the
140.Fn setstate
141routine provides for rapid switching between states.
142The
143.Fn setstate
144function
145returns a pointer to the previous state array; its
146argument state array is used for further random number generation
147until the next call to
148.Fn initstate
149or
150.Fn setstate .
151.Pp
152Once a state array has been initialized, it may be restarted at a
153different point either by calling
154.Fn initstate
155(with the desired seed, the state array, and its size) or by calling
156both
157.Fn setstate
158(with the state array) and
159.Fn srandom
160(with the desired seed).
161The advantage of calling both
162.Fn setstate
163and
164.Fn srandom
165is that the size of the state array does not have to be remembered after
166it is initialized.
167.Pp
168With 256 bytes of state information, the period of the random number
169generator is greater than
170.if t 2\u\s769\s10\d,
171.if n 2**69
172which should be sufficient for most purposes.
173.Sh DIAGNOSTICS
174If
175.Fn initstate
176is called with less than 8 bytes of state information, or if
177.Fn setstate
178detects that the state information has been garbled, error
179messages are printed on the standard error output.
180.Sh SEE ALSO
181.Xr arc4random 3 ,
182.Xr lrand48 3 ,
183.Xr rand 3 ,
184.Xr random 4
185.Sh HISTORY
186These
187functions appeared in
188.Bx 4.2 .
189.Sh AUTHORS
190.An Earl T. Cohen
191.Sh BUGS
192About 2/3 the speed of
193.Xr rand 3 .
194.Pp
195The historical implementation used to have a very weak seeding; the
196random sequence did not vary much with the seed.
197The current implementation employs a better pseudo-random number
198generator for the initial state calculation.
| 30.\"
31.Dd April 2, 2013
32.Dt RANDOM 3
33.Os
34.Sh NAME
35.Nm random ,
36.Nm srandom ,
37.Nm srandomdev ,
38.Nm initstate ,
39.Nm setstate
40.Nd better random number generator; routines for changing generators
41.Sh LIBRARY
42.Lb libc
43.Sh SYNOPSIS
44.In stdlib.h
45.Ft long
46.Fn random void
47.Ft void
48.Fn srandom "unsigned long seed"
49.Ft void
50.Fn srandomdev void
51.Ft char *
52.Fn initstate "unsigned long seed" "char *state" "long n"
53.Ft char *
54.Fn setstate "char *state"
55.Sh DESCRIPTION
56.Bf -symbolic
57The functions described in this manual page are not cryptographically
58secure.
59Cryptographic applications should use
60.Xr arc4random 3
61instead.
62.Ef
63.Pp
64The
65.Fn random
66function
67uses a non-linear additive feedback random number generator employing a
68default table of size 31 long integers to return successive pseudo-random
69numbers in the range from 0 to
70.if t 2\u\s731\s10\d\(mi1.
71.if n (2**31)\(mi1.
72The period of this random number generator is very large, approximately
73.if t 16\(mu(2\u\s731\s10\d\(mi1).
74.if n 16*((2**31)\(mi1).
75.Pp
76The
77.Fn random
78and
79.Fn srandom
80functions have (almost) the same calling sequence and initialization properties as the
81.Xr rand 3
82and
83.Xr srand 3
84functions.
85The difference is that
86.Xr rand 3
87produces a much less random sequence \(em in fact, the low dozen bits
88generated by rand go through a cyclic pattern.
89All the bits generated by
90.Fn random
91are usable.
92For example,
93.Sq Li random()&01
94will produce a random binary
95value.
96.Pp
97Like
98.Xr rand 3 ,
99.Fn random
100will by default produce a sequence of numbers that can be duplicated
101by calling
102.Fn srandom
103with
104.Ql 1
105as the seed.
106.Pp
107The
108.Fn srandomdev
109routine initializes a state array using
110pseudo-random numbers obtained from the kernel.
111Note that this particular seeding
112procedure can generate states which are impossible to reproduce by
113calling
114.Fn srandom
115with any value, since the succeeding terms in the
116state buffer are no longer derived from the LC algorithm applied to
117a fixed seed.
118.Pp
119The
120.Fn initstate
121routine allows a state array, passed in as an argument, to be initialized
122for future use.
123The size of the state array (in bytes) is used by
124.Fn initstate
125to decide how sophisticated a random number generator it should use \(em the
126more state, the better the random numbers will be.
127(Current "optimal" values for the amount of state information are
1288, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
129the nearest known amount.
130Using less than 8 bytes will cause an error.)
131The seed for the initialization (which specifies a starting point for
132the random number sequence, and provides for restarting at the same
133point) is also an argument.
134The
135.Fn initstate
136function
137returns a pointer to the previous state information array.
138.Pp
139Once a state has been initialized, the
140.Fn setstate
141routine provides for rapid switching between states.
142The
143.Fn setstate
144function
145returns a pointer to the previous state array; its
146argument state array is used for further random number generation
147until the next call to
148.Fn initstate
149or
150.Fn setstate .
151.Pp
152Once a state array has been initialized, it may be restarted at a
153different point either by calling
154.Fn initstate
155(with the desired seed, the state array, and its size) or by calling
156both
157.Fn setstate
158(with the state array) and
159.Fn srandom
160(with the desired seed).
161The advantage of calling both
162.Fn setstate
163and
164.Fn srandom
165is that the size of the state array does not have to be remembered after
166it is initialized.
167.Pp
168With 256 bytes of state information, the period of the random number
169generator is greater than
170.if t 2\u\s769\s10\d,
171.if n 2**69
172which should be sufficient for most purposes.
173.Sh DIAGNOSTICS
174If
175.Fn initstate
176is called with less than 8 bytes of state information, or if
177.Fn setstate
178detects that the state information has been garbled, error
179messages are printed on the standard error output.
180.Sh SEE ALSO
181.Xr arc4random 3 ,
182.Xr lrand48 3 ,
183.Xr rand 3 ,
184.Xr random 4
185.Sh HISTORY
186These
187functions appeared in
188.Bx 4.2 .
189.Sh AUTHORS
190.An Earl T. Cohen
191.Sh BUGS
192About 2/3 the speed of
193.Xr rand 3 .
194.Pp
195The historical implementation used to have a very weak seeding; the
196random sequence did not vary much with the seed.
197The current implementation employs a better pseudo-random number
198generator for the initial state calculation.
|